The disclosure of Japanese Patent Application No. 2001-088919 filed on Mar. 26, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates generally to a joining structure in which two or more resin parts are joined together to form an integral resin product or article, and more particularly to a joining structure of resin parts which are joined together by friction welding, such as orbital welding, that utilizes heat generated by friction between joining members (i.e., the resin parts). In particular, the invention is concerned with a technique for preventing fragments of the resin parts dispersed or scattered during frictional movements thereof from entering the inside of the resulting resin product.
2. Description of Related Art
In these days, various types of resin parts have been used in a wide range of industrial or technical fields. Some of the resin parts have a final shape or configuration that is too complicated to be achieved only solely by molding. In other cases in which another member or component is mounted within a resin structure, for example, a plurality of sections to be finally integrated into a single resin structure are formed by molding, and are then joined together into the final structure.
Various methods of integrating resin parts have been proposed and actually practiced. These methods can be systematically classified into some groups as shown in FIG. 6. More specifically, resin joining methods are roughly classified into xe2x80x9cbondingxe2x80x9d, xe2x80x9cmechanical fastening or clampingxe2x80x9d, xe2x80x9cweldingxe2x80x9d, and xe2x80x9cinsertxe2x80x9d. A technology for joining two members by use of friction, to which the invention pertains, belongs to the xe2x80x9cweldingxe2x80x9d category, and more particularly to xe2x80x9cthermal weldingxe2x80x9d. The xe2x80x9cthermal weldingxe2x80x9d is classified into xe2x80x9cexternal heatingxe2x80x9d and xe2x80x9cinternal heatingxe2x80x9d. The technology to which the invention relates belongs to xe2x80x9cinternal heatingxe2x80x9d, and more particularly to xe2x80x9cfriction weldingxe2x80x9d, such as xe2x80x9cultrasonic weldingxe2x80x9d, xe2x80x9cvibration weldingxe2x80x9d, xe2x80x9corbital weldingxe2x80x9d and xe2x80x9cspin weldingxe2x80x9d, with which parts are joined into a product or an article by utilizing frictional heat.
Among various parts of a fuel supply system of a vehicle engine, for example, certain products, such as a fuel pump and a fuel filter, are more likely to be mounted within a fuel tank so as to satisfy fuel vapor gas regulations in recent years, though they were conventionally mounted outside the tank. Upon final assembling of these parts, the above-indicated products may be subjected to a drying process after mounted within the tank, and therefore the products are required to be highly resistant to heat having a temperature that is much higher than that required in the case where the products are mounted outside the tank. To meet this requirement, the products need be made of materials having high heat resistance, including, for example, reinforced resins, such as PA resin, into which glass fibers, or the like, are mixed. In addition to the products or parts located inside the tank, products or parts located outside the tank are also desired to be made of materials having higher heat resistance, in order to achieve improved durability of the fuel supply system.
Among various friction welding technologies as described above, orbital welding, in particular, is suitably employed for joining parts made of resin having high heat resistance. The basic principle of the orbital welding for joining two parts is illustrated in FIGS. 7A, 7B and 7C. More specifically, one of the two parts undergoes minute circular vibratory motions in a horizontal plane (i.e., in a plane of abutting surfaces of the two parts) while the one part is pressed against the other part, so that the two parts are welded to each other with fused resin between their abutting surfaces. As shown in FIG. 7A, a member A is placed on a member B that is held stationary. Then, the member A is subjected to minute circular vibrations while being pressed against the member B, as shown in FIG. 7B. At this time, the vibrations occur in a plane (i.e., a plane of the abutting surfaces), causing friction of a constant velocity at the abutting surfaces, thus permitting uniform welding. As a result, heat generated by the friction normally fuses the abutting surfaces of the parts in several seconds, and the parts are automatically positioned at their positions where the vibrations stopped. After holding the parts under pressure for one to two seconds, during which resin solidifies, the welding process is finished. In this manner, a welded product as shown in FIG. 7C is completed.
The orbital welding is carried out in the manner as described above, and is particularly advantageous in the following six points:
1. The orbital welding enables joining of parts having various shapes, allowing an increased freedom in the shape or design of the parts.
2. The abutting surfaces of the parts are uniformly welded.
3. The resin part to be welded may include a flange having a small width, permitting a burr to be uniformly formed upon welding.
4. The strength of the welded portion is stable.
5. An acceleration G that appears during welding due to constant-velocity motion of the resin part is 10G or smaller, causing almost no stress to the base on which the parts are mounted.
6. The orbital welding can be employed for a wide range of materials, including those having high heat resistance.
Thus, the orbital welding is suitably employed for joining two members when producing various parts to be installed on vehicles as described above.
FIGS. 8A-8C illustrate a typical example in which two parts are joined together by orbital welding. More specifically, a lower member 30 has a flange 31 that is formed with an upper protrusion 32 to be welded, and an inside projecting wall 33 and an outside projecting wall 34 are formed on the opposite sides of the upper protrusion 32 to thus form an inside groove 35 and an outside groove 36. On the other hand, an upper member 37 to be welded and fixed onto the first member 30 has a flange 38 that is formed with a lower protrusion 39 to be welded. As shown in FIG. 8A, the first member 30 and the second member 37 are assembled together such that the lower protrusion 39 of the second member 37 abuts on the upper protrusion 32 of the first member 30.
Next, according to the orbital welding method as shown in FIGS. 7A, 7B and 7C, the upper member 37 is subjected to minute circular vibrations while being pressed against the lower member 30. At this time, minute fragments of the resin parts are produced at abutting portions of the upper protrusion 32 and the lower protrusion 39 where frictional vibrations occur. The properties of the fragments vary depending upon the material of the parts to be welded, degree of frictional vibrations, pressing force, and so forth. In any event, the size of the fragments decreases as the heat resistance and rigidity of the welded material increases. In particular, a large number of fragments are likely to be produced when a reinforced resin, such as PA resin, containing glass fibers is used. As shown in FIG. 8B, many of the fragments 40 produced due to the vibrations fall into the inside groove 35 and the outside groove 36 formed on the opposite side of the upper protrusion 32, but part of the fragments 40 pop out of the inside groove 35 and the outside groove 36, overpassing the inside projecting wall 33 and the outside projecting wall 34, respectively. If the product in question is in the form of a container, fragments that pass the inside projecting wall 33 enter the interior of the container.
Upon completion of the welding process in which minute circular vibrations are applied as described above, a welded product as shown in FIG. 8C is provided. When this product is moved or in use, the fragments 40 accumulated in the bottoms of the inside groove 35 and the outside groove 36 may fall out of these grooves 35, 36, and enter the inside of the container. If the container-shaped product is, for example, a fuel cut valve, a liquid level sensing valve, a tank pressure control valve, or the like, of a fuel vapor gas treating device of a fuel system of a vehicle, such minute fragments entering the container may adhere to functional or operating portions of these products, resulting in, for example, a sealing failure at a valve portion, which may cause a liquid fuel to flow out of the system.
The above-described problem encountered in the above-described known joining structure may be partially solved by an arrangement as shown in FIGS. 9A, 9B and 9C by way of example. In the joining structure of FIG. 9A, inside projecting wall 41 and outside projecting wall 42 formed on the opposite sides of the upper protrusion 32 of the lower member 30 have a greater height than the above-described inside projecting wall 33 and outside projecting wall 34 as shown in FIG. 8A. Thus, the inside and outside projecting walls 41, 42 formed with sufficiently large height function to prevent scattering of fragments of parts to be welded. The heights of the inside and outside projecting walls 41, 42 are determined such that the inside projecting wall 41 and the outside projecting wall 42 abut on a bottom surface 43 of the flange 38 of the upper member 37 at the time of completion of the welding process of the parts, as shown in FIG. 9C.
After the parts as shown in FIG. 9A are welded together into a product, the fragments 40 of the parts accumulated in the inside groove 35 during welding are prevented from passing the inside projecting wall 35 and falling into the inside of the container during transportation of the product or during use as in the case of FIG. 8C. Furthermore, the increase in the height of the inside projecting wall 41 leads to reduction in the amount of fragments 40 that pop out of the inner and outer grooves 35, 36, over the respective projecting walls 41, 42, while minute circular vibrations are being applied to the upper member 37 as shown in FIG. 9B.
However, even with the height of the inside and outside projecting walls 41, 42 increased as described above, some of the fragments 40 overpass the inside projecting wall 41 and pop into the inside of the container, as shown in FIG. 9B. In this case, the fragments may adhere to various valves of the fuel system as described above, thus causing a problem, such as a sealing failure.
It is therefore an object of the invention to provide a joining structure of resin parts, which structure is able to prevent fragments of the parts produced due to friction at the interface from entering a joining portion or the interior of a resulting product when the resin parts are joined together by frictional welding, such as orbital welding.
To accomplish the above and/or other object(s), there is provided according to one aspect of the invention a joining structure which comprises: (a) a first resin member and a second resin member having respective joining portions that are joined together by friction welding, and (b) a projecting wall that is opposed to the joining portions of the first and second resin members with a spacing therebetween. In the joining structure, at least one notch is formed in a surface of the projecting wall that faces the joining portions of the first and second resin members.
When the resin members are joined together by friction welding, such as orbital welding, fragments of the resin members are produced by frictional forces, and are scattered around during welding. With the joining structure as described above, the fragments hit against walls of the notches, and are thus prevented from overpassing the upper end face of the projecting wall and popping out of the structure.
In one preferred embodiment of the invention, the projecting wall is formed as an integral part of one of the first and second resin members. In this case, the end face of the projecting wall may abut on an opposed surface of the other resin member at the time of completion of joining, so that fragments of the first and second resin members are confined in a space between the joining portions and the projecting wall. Consequently, the fragments are prevented from popping out of the structure during movements or use of the resulting product.
According to another aspect of the invention, there is provided a joining structure which comprises: (a) a first resin member and a second resin member having respective joining portions that are joined together by frictional welding, (b) a projecting wall that is opposed to the joining portions of the first and second resin members with a spacing therebetween, and (c) a liquid received in a bottom portion of a space defined between the projecting wall and the joining portions. With this joining structure, fragments of the resin members produced by frictional forces adhere to the liquid, and are thus surely prevented from overpassing the upper end face of the projecting wall and popping out of the structure.
In one preferred embodiment of the above aspect of the invention, at least one notch is formed in a surface of the projecting wall that faces the joining portions of the first and second resin members. In this case, the notches of the projecting wall and the liquid cooperate with each other to prevent scattering of the fragments with further improved reliability by the notches of the projecting wall and the liquid.